Medical apparatus for the therapeutic treatment of an insufficient cardiac valve

ABSTRACT

The present invention relates to a medical apparatus for the therapeutic treatment of an insufficient cardiac valve ( 3   a   , 3   b ). The aim of the present invention is to specify a medical apparatus which enables the therapeutic treatment of an insufficient cardiac valve, such as, for example, the mitral valve ( 3   a ) or the tricuspid valve ( 3   b ), which is arranged between a ventricle ( 1   a,    1   b ) and an atrium ( 2   a   , 2   b ) of the heart, in a manner as simple as possible and as gentle as possible for the patient in a minimally invasive intervention. For this purpose, the medical apparatus according to the present invention comprises at least one valve means ( 10 ) which is designed to prevent in the implanted condition of the medical apparatus a systolic venous reflex return of blood from the atrium ( 2   a,    2   b ) of the heart into at least one vein ( 4   a,    4   a′,    4   b,    4   b′,    4   c,    4   c ′) which belongs to a venous system ( 4 ) which leads into the atrium ( 2   a,    2   b ) of the heart.

The present invention relates to a method and medical apparatus for thetherapeutic treatment of a cardiac valve insufficiency.

As the body ages, cardiac valves can become functionally defective,whether through calcification, genetic faults or general weakness. Inthis way, the valves become stenosed (narrowed), insufficient (unable toclose properly) or a combination of the two (combined vitium).

Current treatment for severe valvular insufficiency is replacement ofthe diseased cardiac valve with a valvular prosthesis. Biological ormechanical valve models are available which are typically surgicallystitched (sutured) to the native cardiac valve bed after opening thethorax and removing the native diseased cardiac valve. During such anintervention, the cardiovascular system of the patient has to besupported by a heart-lung machine, with cardiac arrest being inducedduring implantation of the replacement valvular prosthesis. Thisinvolves a risky surgical intervention with corresponding risks for thepatient and a long postoperative treatment phase. In particular,patients suffering from cardiac insufficiencies may not be fit or wellenough to survive such an invention.

As a result, there is an ongoing effort in the field of medicalengineering to find alternative ways to treat valvular heart disease,for example, by transarterial delivery of a replacement prosthesis,thereby avoiding the potentially life-threatening procedures of openingof the thorax dose and inducing cardiac arrest. An additionalsignificant advantage of minimally invasive therapy methods is that asignificantly reduced anaesthesia time period is required for theintervention. One approach provides for the implantation of aself-expanding valvular prosthesis in which an artificial cardiac valveis held within a foldable and expandable structure such as a stent. Sucha self-expanding valvular prosthesis may be guided by a catheter system,for example through an inguinal artery or inguinal vein, as far as theimplantation site in the heart. After the implantation site has beenreached, the stent is unfolded and anchored in the position of thenative, failing valve. Such a method leaves the native valve in placeand provides a replacement valve in place of the native valve.

The above described method is particularly suited for the treatment ofdiseased semilunar valves, such as the aortic valve or the pulmonaryvalve, i.e. a cardiac valve that lies between a ventricle and adischarge vessel (aorta or pulmonary artery, respectively).

However, such a method is not readily applicable to the treatment ofdiseased atrioventricular valves of the heart. Firstly, theatrioventricular valves of the heart, such as the tricuspid valve or themitral valve, cannot be directly reached with a catheter system via ablood vessel because the valves are located between an atrium andventricle of the heart. In addition, both the mitral valve and thetricuspid valve belong to a valve type which comprises two or three,respectively, relatively delicate, fibrous cusps which are attached viatendinous fibres to the papillary muscles which face the ventricle.

Due to these anatomic facts, therapeutic treatment of mitral ortricuspid valve insufficiency is presently not possible by means of thecurrently available minimally invasive replacement approaches.

Therefore, such insufficiencies are typically treated with a long-termdrug treatment including ACE blockers and often require additionalanti-arrhythmia treatment. This pharmaceutical approach is based on thefinding that patients with a “real”, i.e. not only a physiologicalmitral or tricuspid insufficiency, are at an increased risk of bacterialendocarditis.

Operative therapy is available in which the insufficient cardiac valveis either reconstructed or an artificial cardiac valve is inserted.This, however, entails risky surgical intervention with correspondingrisks for the patient and a long postoperative treatment phase.Moreover, such an invention cannot be performed on patients sufferingfrom other cardiac insufficiencies. Therefore, operative therapy of amitral or tricuspid insufficiency is performed only seldomly.

Accordingly, the present invention arises from the problem of providinga medical apparatus which is suited for the therapeutic treatment orreplacement of an atrioventricular (mitral or tricuspid) valveinsufficiency in such a way that the drawbacks and risks associated withthe currently available options are substantially eliminated. Such amedical apparatus should enable the therapeutic treatment or replacementof an insufficient atrioventricular valve in a manner that is as simpleand as gentle as possible for the patient with minimally invasiveintervention.

This object is solved by a medical apparatus for the therapeutictreatment of an insufficient cardiac valve which is arranged between aventricle and an atrium of the heart, with the medical apparatusaccording to invention comprising at least one valve which is designedto prevent in the implanted condition of the medical apparatus asystolic venous reflex return of blood from the atrium of the heart intoat least one vein which belongs to a venous system which leads into theatrium of the heart. Specifically, the apparatus is suitable for thetreatment of an insufficient atrioventricular valve located between aheart ventricle and atrium, the apparatus comprising at least one pairof valves. Ideally each valve in the pair of valves is directionallyopposed to the other valve in the pair.

It is generally known from the medical science that, in the case of asevere mitral insufficiency or tricuspid insufficiency, serious andsometimes life-threatening changes have to be expected if, for example,the regurgitation opening is greater than 40 mm² and the regurgitationvolume more than 60 ml. Specifically, in the acute stage of a mitralinsufficiency or tricuspid insufficiency, the pressure in the atrium ofthe heart and thus in the veins of the venous system which lead into theatrium of the heart will increase considerably due to the systolicreflex return of blood. With a tricuspid valve insufficiency, thepressure increase in the right-hand atrium of the heart may amount up to50 mm Hg which, with a normal constitution of the venea cavae (superiorand inferior vena cava), results in immediate congestion in the liver ora venous congestion into the cervical vein. In addition, the thendominating reflex return of blood may cause a poor output into thepulmonary artery and thus inadequate circulation to all organs. In thecase of a severe mitral insufficiency, the pressure increase in theleft-hand atrium of the heart may amount up to even 100 mm Hg which,with normal constitution of the pulmonary vessels, leads to immediatepulmonary oedema. In addition, the reflex return of blood may result inpoor output into the aorta and thus again inadequate circulation to allorgans.

The inventive solution is based on the finding that, due to the anatomicpeculiarities of the mitral and tricuspid valves—collectively termed“atrioventricular valves”—a minimally invasive replacement of aninsufficient atrioventricular valve where the diseased atrioventricularvalve is replaced by an artificial valvular prosthesis, is not possibleor possible only at high risk. In the present invention it has beenfound that, for the treatment of a mitral or tricuspid valveinsufficiency, it is not mandatory to replace the diseased cardiac valvewith a valvular prosthesis. Indeed, it is sufficient to provide areplacement apparatus by means of which the normal valve function of theinsufficient atrioventricular valve can be maintained.

Consequently, the proposed inventive solution will combat a more or lesspronounced closure inability or leakiness of a diseased atrioventricularvalve of the heart. In particular, the medical apparatus effectivelyprevents reflex return of blood from the ventricle into the atriumduring the output phase (systole) such that regurgitation of blood intothe venous system can no longer occur. The proposed medical apparatus ofthe present invention is therefore used for the therapeutic treatment ofan insufficient atrioventricular valve or an insufficient cardiac valvewhich is arranged between a ventricle and an atrium of the heart,whereby it is not the diseased cardiac valve itself that is treated orreplaced but an implant is used which is functionally matched to thediseased cardiac valve. This implant is designed to at least partiallyfulfil or support the function of the insufficient cardiac valve withoutthe diseased cardiac valve being replaced or mechanically modified.

Due to the fact that the function of the diseased or insufficientcardiac valve is restored by means of an implant, systolic regurgitationof blood from the atrium of the heart into the veins which lead into theatrium can be effectively prevented. The proposed solution can thuseffectively counteract the danger of congestion in the liver or venouscongestion in the cervical vein, in the case of a tricuspidinsufficiency, or the danger of a pulmonary oedema in the case of amitral insufficiency. Due do the fact the proposed medical apparatusserves to restore the normal function of the cardiac valve, there islittle need to implant the medical apparatus into the immediate vicinityof the diseased cardiac valve. In contrast, the implantation site of themedical apparatus is spatially separated from the site of theinsufficient cardiac valve that is to be treated.

Specifically, it is provided according to the invention that the medicalapparatus comprises at least one pair of valves that is dimensioned forlocation in a vena cava or pulmonary vein. Expressed in another way, theat least one valve is implanted either into the atrium of the heartwhich is separated from the ventricle via the diseased cardiac valve, oris implanted into at least one of the veins belonging to the venoussystem which leads into the atrium which is separated from the ventriclevia the diseased cardiac valve, or is implanted into the pulmonary veinsdraining blood from the pulmonary circulation into the left atrium (Animplantation through the vein is preferred; however, an implantationusing an arterial access (retrograde) is also possible).

The term “venous system” as used herein refers to the group of veinswhich lead into the heart atria. When the tricuspid valve, locatedbetween the right-hand atrium of the heart and the right-hand ventricle,is to be treated, the venous system is thus the superior (upper) venacava and the inferior (lower) vena cava. If the cardiac valve to betreated is the mitral valve, which is located between the left-handatrium of the heart and the left-hand ventricle, the venous systemgenerally comprises four pulmonary veins through which oxygen-rich(arterial) blood from the pulmonary circulation flows to the left-handatrium of the heart.

The inventive solution for the therapeutic treatment of an insufficientcardiac valve which is arranged between a ventricle and an atrium of theheart proposes a medical apparatus which comprises at least one valve,ideally at least one pair of valves which, in the implanted condition,serves to and is designed to prevent a systolic venous reflex return ofblood from the atrium of the heart into at least one vein belonging tothe venous system which leads into the atrium. Due to the fact that thevalve of the medical apparatus is designed to prevent the regurgitationof blood into the associated venous system, which occurs with aninsufficient mitral valve or tricuspid valve, it is possible to implantthe at least one valve away from the immediate vicinity of theinsufficient cardiac valve, in the or in the vicinity of the atrium ofthe heart which is separated from the ventricle via the insufficientcardiac valve.

Because the veins of the venous system which leads into the atrium ofthe heart are normally well suited for probing by means of catheters, amedical apparatus is proposed by the inventive solution by means ofwhich the at least one valve or pair of valves can be implanted in aminimally invasive manner. The proposed medical apparatus thus enables aminimally invasive therapeutic method which, in particular, excels inthat the intervention may be performed under local anaesthesia. It wouldbe conceivable to implant the valves of the medical apparatus in afolded condition via a corresponding catheter system into the atrium ofthe heart or in the respective veins of the venous system which leadsinto the atrium of the heart. Such self-expandable valves may be guidedthrough a peripheral artery or a peripheral vein as far as theimplantation site in the heart by means of a catheter system. Theperipheral artery or vein can be an inguinal, jugular or subclavianartery or vein. After the implantation site has been reached, the valvesmay be unfolded. After unfolding, the valves may be anchored at least inthe atrium-near area of the respective veins of the venous system bymeans of anchoring hooks, barbs or sutures.

As suitable valves, various natural, biological or mechanical valvemodels may be taken into consideration. For example, a natural arterialvalve, such as a semilunar valve, may be used. These may be eithersurgically sutured to the vascular wall of the vein or attached inanother suitable manner. It would also be conceivable that the valves ofthe medical apparatus are held in the implantation site by means of asupport, such as a suitable stent. Thereby, it is of importance that thevalves substantially prevent systolic reflex return of blood from theatrium of the heart into the associated vein of the venous system.

As a possible realisation of the valves, a pressure driven check valvemay be considered which is designed automatically to block thethrough-flow of blood from the atrium during the systole into at leastone associated vein. A check valve is a valve that allows fluid to flowthrough it in only one direction. Check valves are two-port valves,meaning they have two openings in the body, one for fluid (e.g. blood)to enter and the other for fluid (e.g. blood) to leave.

Regardless of the valve model which is employed as a valve, it should benoted that, during implantation of the valves, it is not necessary tosupport the cardiovascular system of the patient on a heart-lungmachine. In particular, it is no longer necessary to induce a cardiacarrest during the procedure. The therapeutic treatment of aninsufficient cardiac valve (atrioventricular valve) which may beachieved with the inventive medical apparatus thus also comprises aninstrument which may be operated in a relatively easy manner and whichis capable of being implanted in a minimally invasive interventionwithout a long postoperative treatment phase. Such an intervention isalso possible for polypathic patients at a justifiable risk.

As valves for the inventive medical apparatus, models may be chosenwhich comprise mechanic valve flaps manufactured from a biologic orsynthetic material, or native valve flaps taken from natural arterialvalves. In particular, it would be conceivable to make the valve flapsfrom metal, synthetic material, or animal tissue. Valve flaps made fromendogenous tissue are, of course, also conceivable. Such valve flapshave the decisive advantage that no (higher) risk of embolism exists sothe patient should not need to be prescribed anti-coagulant medication.It is known that the administration of anti-coagulants increases thedanger of bleeding from the stomach and cerebral bleedings and so is anundesirable outcome.

As already mentioned, a plurality of veins belongs to the venous systemlead into the atria of the heart. Specifically, the venous system whichleads into the right-hand atrium comprises the superior and inferiorvena cava, via which deoxygenated (venous) blood from the systemiccirculation is supplied to the heart. The tricuspid valve separates theright atrium from the right ventricle. On the other hand, generally fourpulmonary veins belong to the pulmonary system lead into the left-handatrium of the heart, which is separated from the left-hand ventricle viathe mitral valve. For an effective therapeutic treatment of aninsufficient cardiac valve which is arranged between a ventricle and anatrium of the heart it is mandatory that a systolic reflex return ofblood into each single vein of the venous system which leads into theatrium of the heart is prevented by means of the medical apparatus. Forthis purpose it would be conceivable that the at least one valve meansof the medical apparatus is correspondingly designed and dimensioned forsimultaneously preventing a regurgitation of blood from the atrium ofthe heart into several veins of the venous system. This seems to beobvious, in particular, if the veins of the venous system are arrangedin a neighbouring relationship as in the case of the venous system whichleads into the left-hand atrium of the heart. In this venous system, twopulmonary veins extend almost in parallel into the left-hand atrium ofthe heart so that a systolic reflex return of blood from the left-handatrium of the heart into these two parallel pulmonary veins may beprevented by a single valve means, in that said valve means covers themouth area of both pulmonary veins.

For anatomic reasons, however, it is not possible that a single valvealways covers several veins of a venous system simultaneously. Thisapplies in particular in those cases in which the respective mouth areasof the veins into the atrium of the heart are relatively remote from oneanother. In the right-hand atrium of the heart, for example, the uppervena cava enters the top of the atrium, while the mouth of the lowervena cava is located almost opposite in the lower portion of the atrium.In such a case it is preferred that the medical apparatus comprises acorrespondingly assigned valve for each vein which leads into theatrium, with the dimension of the respective valve being matched to thediameter of the associated vein.

As already mentioned, it is conceivable to attach the valves of themedical apparatus after its implantation by means of threads, hooks,barbs or clamps at the vascular wall of a vein. Alternatively, one orseveral stents might be provided for the attachment of the valves at theimplantation site(s). Such stents may preferably be inserted into thebody of the patient in a minimally invasive manner and may either beimplanted or fixed a vein of the venous system or in the atrium of theheart into which the vein leads. The at least one valve should beattached inside the stent or in a proximal retention area of the stent.

If the medical apparatus comprises a stent which serves to and isdesigned to be implanted into a vein of the venous system leading intothe atrium of the heart, preferably near the mouth area of the vein intothe atrium of the heart, it would be conceivable to attach the valve ina central area of the stent. In this way, stable and reliable anchoringof the valve is ensured. It is, of course, also conceivable that the atleast one stent of the medical apparatus is designed in such a mannerthat, in the implanted condition, it extends only partially into thevein and is held by the vascular wall of the area near the mouth of thevein, while the proximal end portion of the stent protrudes into theatrium of the heart with the valve being attached at the proximal endportion of the stent.

It is principally applicable that the valve should be arranged relativeto the stent and connected in such a manner that, in the implantedcondition of the stent, the valve is able effectively to preventregurgitation of blood from the atrium of the heart into the at leastone associated vein.

In a further embodiment of the inventive apparatus which comprises atleast one stent for holding and fixing each valve, it is advantageous toprovide the at least one stent with an expandable structure. Ideally,the diameter of the at least one stent in its expanded condition ismatched to the diameter of the vein in which the stent is to beimplanted. Due to its preferably expandable structure, the stent in itsfolded condition may be advanced via a catheter system in a minimallyinvasive manner to the implantation site in the heart. After havingreached the implantation site, the stent which, in the longitudinaldirection, may also be composed of several stent segments which may bebent under an angle relative to one another and are self-expanding, maybe successively unfolded. After unfolding, the valve may be attached toor inside the stent, for example with the aid of fastening hooks, in thearea near the mouth of the appropriate vein.

It is, of course, also conceivable that the valve is already securelyconnected with the stent and able to be folded together with the stentin order to enable the implantation of these two systems.

Because the stent in its expanded condition is matched to the diameterof the vein to the stent is assigned, it is possible to hold the stentreliably together with the valve, the valve be attached or attachable tothe stent without additional auxiliary means at the site ofimplantation. It is advantageous if the stent in its implanted andexpanded condition presses against the vascular wall of the vein with arelatively small radially acting force. This radially acting forceserves to hold the stent reliably in its implanted position. In thedesign of the stent, on the other hand, care should be taken not to usean excessive radial force to avoid damage to the vascular wall of thevein.

To enable a reliable fixing of the stent at the site of implantation, itis possible to provide the stent with a plurality of distributedanchoring hooks or barbs on its outside which, in the implantedcondition of the stent, engage with the vascular wall of the veinassigned to the stent and thus ensure an especially reliable anchoringof the stent.

For the at least one stent of the inventive medical apparatus, variousstent types may be considered, including stents formed from a braid ofthin wires or threads. Stent types which are cut as one piece from asmall metal tube and then appropriately treated are, of course, alsosuitable. As the material for the stent, the usual solutions which areknown from medical engineering may be taken into consideration. Inparticular, however, a shape memory material, such as nitinol or a shapememory polymer material, is a preferred choice, so that the stentcomprises a self-expandable structure. It is, of course, also possibleto form the stent from a material which has no shape memory capability.With such a stent type, the expansion of the stent in the implantationsite is to be effected by an external manipulation, for example by usinga balloon catheter.

As already mentioned, the medical apparatus should preferably comprise aplurality of valves, with each valve being assigned to a vein of thevenous system which leads into the atrium. If the medical apparatuscomprises at least one stent for establishing the position of the valvein the venous system or in the atrium of the heart and for anchoring thevalve in the implantation site, it is advantageous if the medicalapparatus comprises for each vein one stent with an attached orattachable valve. The respective stents are capable of being implantedeither successively or simultaneously into the venous system by means ofone and the same catheter system.

It is advantageous to connect the individual stents of the medicalapparatus to each other via one or more supporting braces. Thesesupporting braces may already be connected with the individual stentsprior to implantation of the individual stents. However, it is alsopossible to arrange and attach the supporting braces after theimplantation of the individual stents. In the implanted condition of themedical apparatus, the supporting braces extend through the atrium ofthe heart and preferably connect the respective proximal end portions ofthe individual stents The provision of such supporting braces ensures aparticularly reliable fixing of the stents in the respective veins ofthe venous system. The supporting braces primarily serve to secure therelative position of the individual stents in their respective implantedpositions. In this context, it has to be taken into consideration that,due to the insufficient cardiac valve, blood flows back into the atriumof the heart upon the contraction of the heart, resulting in a pressureincrease in the atrium. Because regurgitation of blood from the atriuminto the individual veins leading into the atrium is substantiallyprevented with the aid of the respective valves, it is important thatthe individual valves are reliably fixed, especially during systole, andare not urged in the distal direction into the vein due to the increasedpressure in the atrium of the heart. This may be prevented veryeffectively by way of the supporting braces.

It is, of course, also conceivable that the supporting braces have acertain flexural rigidity to counteract any displacement of theindividual stents in the proximal direction, i.e. towards the atrium ofthe heart.

As an alternative to the previously described embodiment in which themedical apparatus comprises a stent with a valve for each vein of thevenous system, it would be conceivable that the medical apparatuscomprises only one stent which is formed from different stent portions.It might be conceivable that a first stent portion of the stent isprovided and designed or adapted with a first valve for the implantationinto a first vein of the venous system, with the stent furthercomprising a second stent portion with a second valve. This second stentportion may be designed and adapted to be inserted into a second vein ofthe venous system. The two stent portions are preferably connected withone another via at least one supporting brace.

The advantage of the last mentioned embodiment lies in the fact that thestent with its stent portions and the associated valve can be implantedas a single implant using a single intervention procedure.

In the last mentioned embodiment it is, of course, also possible thatthe stent further comprises a third and a fourth stent portion withthird and fourth valves which are designed and adapted to be insertedinto a corresponding third and fourth vein of the venous system.

In a preferred embodiment of the medical apparatus, in which at leastone stent for holding and fixing the valve is employed, at least onestent may be capable of being implanted into the vein system which leadsinto the atrium of the heart in such a manner the at least one valve islocated at the proximal end portion of the stent in the atrium of theheart. This valve should be designed to prevent simultaneouslyregurgitation of blood from the atrium of the heart into at least twoveins of the venous system. This preferred embodiment is suitable forrelatively closely-spaced veins which lead into the atrium of the heart.In such a case, a bifurcated stent may be used which engages the moutharea of both veins and abuts the vascular wall of the respective veinswhere it is held. Thus, the distal end portion of the stent protrudesinto the mouth area of a first vein, on the one hand, and into the moutharea of a second vein. At the proximal end portion, a valve is arrangedand held so that this valve covers the mouth areas of both veins andthus prevents regurgitation of blood from the atrium into both veins.

It will be apparent that the medical apparatus of the present inventionis designed to correct a faulty valve function of an insufficientcardiac valve, in particular a mitral valve or a tricuspid valve, in aminimally invasive intervention. In order to enable a suitableimplantation of the medical apparatus and, in particular, of thecorresponding valve optionally with a stent, the medical apparatusfurther resides in an insertion system for inserting the at least onestent with the valve attached thereon into the body of the patient. Theinsertion system may comprise a catheter system with a catheter tipprovided at the proximal end of the catheter system and a manipulatorprovided at the distal end of the catheter system. The at least onestent with the at least one valve attached is preferably designed to beexpandable and may be accommodated in the catheter tip in a foldedconfiguration. In this manner, the at least one stent, in its foldedconfiguration, can be inserted into body of the patient. The manipulatorprovided at the distal end of the catheter system may be used tomanipulate the catheter tip, via which the at least one stent isreleased and the stent and valve implanted.

After release of the stent from the catheter tip, the stent assumes anexpanded condition, either automatically or with the aid of a suitableauxiliary means such as a balloon catheter, and is anchored at theimplantation site.

It is particularly preferred to use an insertion system by means ofwhich at least one stent with the valve attached thereon can be advancedthrough the vena cava or through a pulmonary vein of a patient to betreated (retrograde or transarterial). Alternatively, the implantationsite may be accessed through the apex of the heart (transapical). Withtransarterial access, the insertion catheter system preferably does notcompletely fill the free cross-section which is available within thevein.

From a yet further aspect, the present invention resides in a method ofreplacing an insufficient atrioventricular valve located between a heartventricle and atrium, the method comprising implanting, at a positionproximate to the atrium, one or more pairs of valves in a vein thatfeeds directly into the atrium.

Expressed in another way, the invention encompasses the use of one ormore pairs of valves substantially to replace or enhance the function ofan insufficient atrioventricular valve located between a heart ventricleand atrium, wherein the valves are implanted in one or more veins at aposition proximate to the atrium.

The method also encompasses the treatment of an insufficientatrioventricular valve located between a heart ventricle and atrium byvenous implantation of at least one pair of valves proximate to theatrium.

Alternatively, the invention resides in the enhancement of tricuspidand/or mitral valve function by the use of at least one pair of valvesvenously implanted at a position proximate to a heart atrium.

Ideally, each valve in the pair of valves is directionally opposed tothe other valve in the pair.

As described above, the vein is the vena cava or pulmonary vein. Forexample, a pair of valves may be implanted in the superior and inferiorvena cava respectively, proximate to where the venae cavae join theright atrium. In this respect, the valve in the superior vena cavasubstantially prevents blood flow from the right atrium into thesuperior vena cava and the valve in the inferior vena cava substantiallyprevents blood flow from the right atrium into the inferior vena cava.

Alternatively, two pairs of valves may be implanted in pulmonary veinsproximate to where the veins join the left atrium. In this embodiment,each valve substantially prevents blood flow from the left atrium in thepulmonary vein.

In the following, preferred embodiments of a medical apparatus for thetherapeutic treatment of an insufficient cardiac valve located between aventricle and an atrium of the heart will be described in more detailwith reference to the accompanying drawings; in which:

FIG. 1 is a schematic view of a first embodiment of the inventivemedical apparatus, which is specifically suited for the therapeutictreatment of a tricuspid insufficiency;

FIG. 2 is a schematic view of a second embodiment of the inventivemedical apparatus, which is specifically suited for the therapeutictreatment of a tricuspid insufficiency;

FIG. 3 is a schematic view of a third embodiment of the inventivemedical apparatus, which is specifically suited for the therapeutictreatment of a mitral insufficiency;

FIG. 4 is a schematic view of a fourth embodiment of the inventivemedical apparatus, which is specifically suited for the therapeutictreatment of a mitral insufficiency; and

FIG. 5 is a schematic view of a fifth embodiment of the inventivemedical apparatus, which is specifically suited for the therapeutictreatment of a mitral insufficiency.

The heart is divided into left and right sides. The function of theright side is to collect de-oxygenated blood, in the right atrium 2 b,from the body and pump it, via the right ventricle 1 b, into the lungs.The left side collects oxygenated blood from the lungs into the leftatrium 2 a. From the left atrium 2 a the blood moves into the leftventricle 1 a which pumps the blood out to the body.

Starting in the right atrium 2 b, deoxygenated blood flows into theatrium 2 b from the superior and inferior vena cava 4 a, 4 a′. Thetricuspid valve 3 a, located between the right atrium 2 b and rightventricle 1 b, is open due to the increased pressure in the atrium 2 band blood flows into the right ventricle 1 b. Atrial systole causesincreased pressure in the atrium 2 b and added blood flow into theventricle 1 b. Pressure in the ventricle 1 b then rises and sooneclipses the pressure in the atrium 2 b, closing the tricuspid valve 3a. The pressure in the ventricle 1 b continues to rise until thepressure in the ventricle 1 b is greater that the pressure in thepulmonary artery 7. This causes the pulmonary semilunar valve 8 a toopen, allowing blood to eject into the pulmonary artery 7 which carriesthe blood to the lungs. As pressure in the ventricle 1 b drops to belowthe pressure in the atrium 2 b, the tricuspid valve 3 a opens, causingblood accumulated in the atrium 2 b to flow into the ventricle 1 b.

From the lungs, blood flows back through the pulmonary vein 4 b, 4 b′ tothe left atrium 2 a. The mitral (also termed “bicuspid”) valve 3 bregulates the flow of blood into the left ventricle 1 a, from where theblood is pumped through the aortic semilunar valve 8 b to the aorta 6.The aorta 6 forks and the blood is divided between major arteries whichsupply the upper and lower body.

FIG. 1 shows a schematic view of a first embodiment of the inventivemedical apparatus for the therapeutic treatment of a tricuspidinsufficiency. More specifically, FIG. 1 schematically shows alongitudinal section of a human heart. In this embodiment, theinsufficient atrioventricular valve which is to be treated by means ofthe medical apparatus is the tricuspid valve 3 a, located between theright-hand atrium 2 b of the heart and the right-hand ventricle 1 b.

The tricuspid valve 3 a consists of three relatively delicate, fibrouscusps which originate from the right-hand anulus fibrosus. The cusps ofthe tricuspid valve 3 a are attached by tendinous fibres 5 (chordaetendineae) to three papillary muscles which face the right-handventricle 1 b. Tricuspid valves may also occur with two or four leafletsand the number may change during life. The largest cusp is interposedbetween the atrioventricular orifice and the conus arteriosus and istermed the anterior or infundibular cusp. A second, the posterior ormarginal cusp, is in relation to the right margin of the ventricle. Athird, the medial or septal cusp, to the ventricular septum. A smallamount of leakage or regurgitation is not uncommon in the tricuspidvalve.

The schematic illustration of FIG. 1 concerns a tricuspid insufficiencyin which the tricuspid valve 3 a no longer closes correctly, completelyor sufficiently during the systolic phase of the heart beat. Due to theleakiness (regurgitation opening) of the valve, when the heart contractsduring systole, blood from the right-hand ventricle 1 b is able to flowback into the right-hand atrium 2 b, as schematically indicated by thedouble arrow in FIG. 1. With a severe tricuspid insufficiency, theregurgitation opening may be larger than 40 mm² and the regurgitationvolume more than 60 ml, which results in a considerable increase inpressure in the right-hand atrium 2 b. In this context, it should benoted that a pressure of normally approx. 4 mm Hg prevails in the atriumwhile, with a severe tricuspid insufficiency, the pressure may be ashigh as 50 mm Hg.

The superior (upper) and inferior (lower) venae cavae 4 a, 4 a′ carryblood from the cervical vein and liver respectively. Therefore, it isimperative that there is no backflow of blood in either vena cava 4 a, 4a′. If the tricuspid valve 3 a is not able to close properly, when theright ventricle 1 b contracts during systole, there is a risk that bloodwill be pushed backwards into the right atrium 2 b, through thepartially closed tricuspid valve 3 a, and into the venae cavae 4 a, 4a′. It will be appreciated that this could lead to congestion in theliver and a venous congestion into the cervical vein. To preventbackflow into the venae cavae 4 a, 4 a′ in such a situation, a pair ofdirectionally opposed valves 10 a and 10 b may be implanted in the venaecavae 4 a, 4 a′ at a position proximate to where the venae cavae 4 a, 4a′ enter the right atrium 2 b. The two valves 10 a, 10 b are preferablypressure driven check valves designed to block automatically thethroughflow of blood during the systole of the heart from the right-handatrium 2 b of the heart into the upper vena cava 4 a or into the lowervena cava 4 a′ of the venous system 4.

The valves 10 which are illustrated in the embodiment shown in FIG. 1,function like a valve between the right-hand atrium 2 b and the twovenae cavae (upper vena cava 4 a, lower vena cava 4 a′) leading into theright-hand atrium 2 b. The valves 10 open during the filling phase ofthe ventricle (diastole), thereby enabling the inflow of blood from thevenous system 4 into the right-hand atrium 2 b. At the beginning of theoutput phase (systole), the increasing pressure in the ventricle alsoresults in a pressure increase in the right-hand atrium 2 b due to theregurgitation opening in the defective tricuspid valve 2 a. Because thevalves 10 are formed as pressure-driven check valves, the pressureincrease in the right-hand atrium 2 b at the beginning of the outputphase causes the closure of the valve flaps 11 of the valves 10, therebysealing the upper and lower vena cava 4 a, 4 a′ from blood flowing inthe wrong direction. In this manner, a pressure increase in the venaecavae 4 a, 4 a′ is prevented during the systole. In fact, because of theimplanted medical apparatus, a pressure of only approx. 4 mm Hg prevailsin the venae cavae 4 a, 4 a′ also during the systole, while at the sametime a pressure exceeding 50 mm Hg may prevail in the right-hand atrium2 b because of the regurgitation opening in the defective tricuspidvalve 3 a.

It is therefore possible to treat a tricuspid insufficiency effectivelywith the medical apparatus according to the present invention, namely inthat the poor or faulty valve or closing function of the tricuspid valve3 a is corrected by the valve means 10 a, 10 b of the medical apparatus.

In the following, the technical details of the first embodiment of theinventive medical apparatus illustrated in FIG. 1 will be explained inmore detail.

In the first embodiment according to FIG. 1, the medical apparatuscomprises a pair of valves 10 a, 10 b which—as already mentioned—arepreferably formed as one-way pressure-driven valves. The valves 10 a, 10b may be fixed in position, in the respective mouth areas of the upperand lower vena cava 4 a, 4 a′, by any suitable means including thread(sutures), barbs or a clamping mechanism. While not essential, thevalves 10 a, 10 b may each be supported by a stent 12 a, 12 b. Theapplication is not limited by the type of stent and any suitable stent,including those described, for example, in DE 10 2005 051 849 A1, U.S.Pat. No. 6,254,564 B, US 2003-0036791 A1 or WO 2004/019825, may be used.

The stents 12 which are illustrated in the accompanying drawings areself-expandable stents throughout, in whose central area or at theproximal end portion at least one valve 10 each is suitably fastened.The two stents 12 a, 12 b in FIG. 1 serve to hold and fix the valves 10a, 10 b in the mouth area of the venae cavae 4 a, 4 a′ which leads intothe right-hand atrium 2 b. It is advantageous if a stent type isemployed which in the expanded condition has a diameter which is atleast equal to the diameter of the vena cava 4 a, 4 a′ into which thestent 12 a, 12 b with the valves 10 a, 10 b fastened thereon is to beimplanted.

It is principally applicable that the stents 12 a, 12 b in the expandedcondition should preferably have a diameter each which is slightlylarger than the cross-section of the associated vena cava 4 a, 4 a′ forreliably fixing the valves 10 a, 10 b. It is then possible that, afterunfolding of the stent 12, it exerts a (small) radial force on thevascular wall of the vena cava 4 a, 4 a′ by means of which the stent 12a, 12 b can be held in position. It is, of course, also conceivable thatthe stents 12 a, 12 b include one or several anchoring hooks or barbswhich are distributed on their outer surfaces and which, in the expandedand implanted condition the stents 12 a, 12 b, engage with the vascularwall of the vena cava 4 a, 4 a′ and thus ensure reliable fixing of thestents 12 a, 12 b.

To achieve a particularly reliable anchoring of the stents 12 a, 12 b inthe respective vena cava 4 a, 4 a′, it is preferred that the stents 12a, 12 b in the manufacturing process are subjected to a forming and heattreatment process so that, in the finished condition of the stents 12 a,12 b, they have a slightly concave structure in the expanded conditionwhich tapers towards the proximal retention area. In other words, theproximal retention area of the stents 12 a, 12 b, i.e. the area wherethe valves 10 a, 10 b are preferably fastened, comprises a slightlytapered diameter compared to the distal retention area.

Specifically, it was found that where the distal retention area of thestent 12 a, 12 b in its expanded condition has a diameter of up toapprox. 10% to 25% larger than the diameter of the proximal retentionarea of the stent 12 a, 12 b, in particular in the distal retention areaof the stent 12 a, 12 b, radial forces are generated which enable areliable grip of the stent 12 a, 12 b with the valves 10 a, 10 b andthus the medical apparatus in the vena cava 4 a, 4 a′. Peristalticmovement of the heart or of the vascular wall is also taken intoaccount. The slightly lower radial force which is exerted from theproximal retention area of the stent 12 a, 12 b does not serve primarilyto anchor the stent 12 a, 12 b or the valve 10 a, 10 b in the vena cava4 a, 4 a′, but to expand the valves 10 a, 10 b which are preferablyarranged near the proximal retention area of the stent 12 a, 12 b andfor reliably sealing the valve against the vascular wall. It will beappreciated that the concave structure of the stent 12 a, 12 b in theexpanded condition may be more or less pronounced.

For the implantation of the medical apparatus according to the firstembodiment, the stents 12 a, 12 b with the valves 10 a, 10 b fastenedthereon are guided via a suitable insertion catheter system through aninguinal artery or vein as far as the implantation site, namely themouth area of the upper or lower vera cava 4 a, 4 a′ of the right-handatrium 2 b. Having reached the implantation site, the stents 12 a, 12 bmay then be successively unfolded. Simultaneously with the unfolding ofthe stent 12 a, 12 b, the valves 10 a, 10 b with their valve flaps 11are expanded.

Because an effective treatment of a tricuspid valve insufficiencyrequires the provision of one valve 10 a or 10 b, respectively, in eachmouth area of the two venae cavae 4 a, 4 a′ which lead into theright-hand atrium 2 b, it is necessary to advance the two valves 10 a,10 b with their associated stents 12 a, 12 b to which the valves 10 a,10 b are fastened, successively into their respective implantationsites. It would, of course, also be possible simultaneously to insertand successively unfold both stents 12 a, 12 b by means of the insertioncatheter system.

FIG. 2 is a schematic illustration of a second embodiment of the medicalapparatus for the treatment of a tricuspid valve insufficiency. Thesecond embodiment of the medical apparatus is essentially identical tothe first embodiment with the exception of the addition of supportingbraces 13 which connect the respective proximal retention portions ofthe two stents 12 a, 12 b with one another. The supporting braces 13serve to fix the two stents 12 a, 12 b, and thus the valves 10 a, 10 b,in a particularly reliable manner.

In this context is has to be taken into consideration that, due to theregurgitation opening in the tricuspid valve 3 a, blood returns intoright-hand atrium 2 b of the heart during the contraction of theventricle (systole), resulting in a marked pressure increase in theright-hand atrium 2 b. Because the valves 10 a, 10 b of the medicalapparatus are designed to close automatically during the output phase(systole), there is a risk that the valves 10 a, 10 b with theassociated stents 12 a, 12 b may be urged in the distal direction intothe respective vena cava 4 a, 4 a′ due to the considerable pressureincrease in the right-hand atrium 2 b. To ensure that minimal positionaldisplacement of the valves 10 a, 10 b of the medical apparatus occursduring the systole, the supporting braces 13 between the proximalretention areas of the two stents 12 a, 12 b are biased, so that therelative distance between the two stents 12 a, 12 b can reliably bemaintained.

The supporting braces 13 may be installed after the implantation of thetwo stents 12 a, 12 b into their respective implantation site at themouth area of the upper or lower vena cava 4 a, 4 a′. It is alsoconceivable that the medical apparatus is implanted with the stents 12a, 12 b already connected via the supporting braces 13.

In the following, a third embodiment of the present invention will bedescribed with reference to FIG. 3. The schematic illustration of FIG. 3shows an embodiment of the medical apparatus for the therapeutictreatment of a mitral valve insufficiency. As can be seen, theinsufficient mitral valve 3 b is disposed between the left-handventricle 1 a and the left-hand atrium 2 a. In the case of a mitralvalve insufficiency, the mitral valve 3 b does not close correctly sothat blood from the left-hand ventricle 1 a is able to flow back intothe left-hand atrium 2 a during systole. Depending on the regurgitationopening as a result of the mitral insufficiency, a considerable pressureincrease occurs in the left-hand atrium 2 a, which may amount to up to100 mm Hg.

The medical apparatus according to the third embodiment effectivelyprevents the pressure increase in the left-hand atrium 2 a frompropagating into the pulmonary veins 4 b, 4 b′, 4 c, 4 c′. Morespecifically, it is provided that the medical apparatus comprises atotal of four valves 10 a to 10 d, with each of the four valves 10 a to10 d being assigned to a pulmonary vein 4 b, 4 b′, 4 c, 4 c′.

Similar to the first embodiment of the medical apparatus, the individualvalves 10 a to 10 d of the embodiment shown in FIG. 3 are supported byway of stents 12 a to 12 d in the respective mouth areas of thepulmonary veins 4 b, 4 b′, 4 c, 4 c′ which lead into left-hand atrium 2a.

In FIG. 4, another embodiment of a medical apparatus for the therapeutictreatment of a mitral insufficiency is shown. The embodiment of themedical apparatus of FIG. 4 is essentially identical to the previouslydescribed embodiment shown in. 3. However, in the fourth embodiment, theindividual stents 12 a to 12 d are connected with each other viasupporting braces 13. As has already been explained in the context ofFIG. 2, these supporting braces 13 are used to hold the stents 12 a to12 d, in particular during systole, in their respective implantationsite.

In FIG. 5, a yet further embodiment of a medical apparatus for thetherapeutic treatment of a mitral insufficiency is shown. In contrast tothe previously described embodiment with reference to FIG. 4, a total ofonly two valves 10 a, 10 b are employed. Each of the two valves 10 a, 10b prevents regurgitation of blood from the left-hand atrium 2 a of theheart into two neighbouring pulmonary veins 4 b, 4 b′ or 4 c, 4 c′,respectively.

Although it would be principally conceivable to suture the valves 10 a,10 b at the implantation site, a stent 12 a, 12 b is ideally employedfor each valve 10 a, 10 b in the embodiment shown in FIG. 5. The valves10 a, 10 b fastened into the stent 12 a, 12 b is suitably positioned andsecured upstream of the two mouth openings of the pairs of pulmonaryveins 4 b, 4 b′ or 4 c, 4 c′, respectively.

Although the above description of the embodiments refer to severalstents which are used for the positioning and fixing of the valve means,it is, of course, also conceivable that only one individual stent isused for the medical apparatus. Such an apparatus may comprise severalstent portions which are, for example, connected to each other viasupporting braces, with each stent portion being assigned at least onevalve means. Each stent portion will also be designed to be implantedinto a vein of the venous system which leads into an atrium of theheart.

As already mentioned, it is also possible to use one or severalself-expandable stents 12. The stent 12 may, for example, comprise anintegral structure which is cut from a small metal tube by means of alaser. Subsequently, the structure may be subjected to a suitableforming and heat treatment process so that the stent can be transferredform a folded configuration during implantation to an expandedconfiguration once at the implantation site. This forming and heattreatment process should advantageously be performed in a stepwisemanner to avoid damage to the stent structure.

It is, of course, also conceivable to use a stent structure consistingof a braid of thin wires or threads.

In a particularly preferred realisation of the medical apparatus, itcomprises at least one stent 12 with the valve 10 fastened thereto withvalve means 10 comprising mechanical valve flaps 11 made from asynthetic material, a metal, or an organic material.

With respect to the material to be used for the stent 12 of the medicalapparatus, a shape memory material is preferably. This provides thestent 12, under the influence of an external stimulus, to transform froma temporary shape to a permanent shape, with the temporary shapeprevailing in the first forming operation of the stent, i.e. in thefolded condition of the medical apparatus, and the permanent shapeprevailing in the second forming operation of the stent, i.e. in theexpanded condition of the medical apparatus. In particular, by using ashape memory material, such as nitinol—an equiatomic alloy of nickel andtitanium—it is possible to implant the medical apparatus in aparticularly gentle, non-abrasive and non-invasive manner

In the manufacture of a stent 12 from a shape memory material it may beprovided that, after cutting the stent structure from a small metaltube, the structure is deformed and fixed in desired temporary shape.This procedure is known as “programming”. This process may, on the onehand, be carried out in such a manner that the stent structure isheated, deformed, and then cooled. On the other hand, the stentstructure may also be deformed at a low temperature, which is known as“cold drawing”. In this operation, the permanent shape is stored, whilethe temporary shape is currently present. If the stent structure issubsequently subjected to an external stimulus, the shape memory effectwill be initiated and thus the stored permanent shape be restored. Bycooling of the stent structure, the temporary shape will be restorednon-reversibly, which is referred to as a so-called “one-way shapememory effect”. The original temporary shape—but other shapes aswell—may be reprogrammed by another mechanical deformation.

In a particularly preferred embodiment it is provided that the externalstimulus is a specifiable transition temperature. It is thereforeconceivable that, for initiating the shape memory effect and thus forrestoring the stored permanent shape of the stent 12, the stent materialhas to be heated to a temperature above the transition temperature. Bysuitably selecting the chemical composition of the shape memorymaterial, a certain transition temperature can be established inadvance.

It is particularly preferred to establish the transition temperature inthe range of the room temperature and the body temperature of thepatient. This is advantageous primarily with respect to the applicationfield of the medical apparatus as an implant in a body of a patient. Inthe implantation of the medical apparatus, the only precaution that hasto taken is to ensure that the instrument is heated to the bodytemperature (36° C.) of the patient in the implanted condition only, andthus the shape memory effect of the stent material is initiated.

The invention is not limited to the characteristics which have beendescribed in connection with the embodiments illustrated in the figures,but allows any combination of the characteristics indicated inspecification.

LIST OF REFERENCE NUMERALS

-   -   1 a left-hand ventricle    -   1 b right-hand ventricle    -   2 a left-hand atrium    -   2 b right-hand atrium    -   3 a tricuspid valve    -   3 b mitral valve    -   4 vein system    -   4 a upper vena cava    -   4 a′ lower vena cava    -   4 b first pulmonary vein    -   4 b′ second pulmonary vein    -   4 c third pulmonary vein    -   4 c′ pulmonary vein    -   5 tendinous fibres    -   6 aorta    -   7 pulmonary artery    -   8 a pulmonary semilunar valve    -   8 b aortic semilunar valve    -   10 valve/valve means    -   11 valve flap    -   12 stent    -   13 supporting brace

1-45. (canceled)
 46. An apparatus comprising: a first stent including afirst valve coupled to a proximal end of the first stent, the proximalend of the first stent having a smaller diameter than a distal end ofthe first stent, wherein the first stent is configured for implantationin a first vein leading to an atrium of a heart such that, whenimplanted, the proximal end of the first stent extends into a portion ofthe atrium, and the distal end of the first stent extends into a portionof the first vein; and a second stent directionally opposed to the firststent, the second stent including a second valve coupled to a proximalend of the second stent, the proximal end of the second stent having asmaller diameter than a distal end of the second stent, wherein thesecond stent is configured for implantation in a second vein leading tothe atrium such that, when implanted, the proximal end of the secondstent extends into a portion of the atrium, and the distal end of thesecond stent extends into a portion of the second vein.
 47. Theapparatus of claim 46, wherein: the first valve, when implanted, permitsblood flow towards the atrium from the first vein, and prevents bloodflow from the atrium to the first vein; and the second valve, whenimplanted, permits blood flow towards the atrium from the second vein,and prevents blood flow from the atrium to the second vein.
 48. Theapparatus of claim 46, wherein each of the first stent and the secondstent is expandable from a collapsed configuration to an expandedconfiguration, such that, a fully-expanded diameter of the proximal endof the first stent is smaller than a fully-expanded diameter of thedistal end of the first stent, and a fully-expanded diameter of theproximal end of the second stent is smaller than a fully-expandeddiameter of the distal end of the second stent.
 49. The apparatus ofclaim 48, wherein at least one of the first stent and the second stentincludes a self-expandable material.
 50. The apparatus of claim 48,wherein at least one of the first stent and the second stent is balloonexpandable.
 51. The apparatus of claim 46, further comprising a bracingelement connecting the first stent to the second stent, the bracingelement extending across the atrium.
 52. The apparatus of claim 46,further including a plurality of bracing elements connecting theproximal end of the first stent to the proximal end of the second stent,wherein each bracing element extends across the atrium.
 53. Theapparatus of claim 46, wherein the first stent is structurallyunconnected from the second stent.
 54. The apparatus of claim 46,wherein each of the first valve and the second valve includes abiological material or a synthetic material.
 55. The apparatus of claim54, wherein at least one of the first valve and the second valveincludes animal tissue.
 56. The apparatus of claim 46, wherein thedistal end of the first stent extends into a portion of a third veinwhen implanted, and wherein the distal end of the second stent extendsinto a portion of a fourth vein when implanted.
 57. The apparatus ofclaim 56, wherein the first valve, when implanted, permits blood flowtowards the atrium from the first vein and the third vein, and preventsblood flow from the atrium to the first vein and the third vein; and thesecond valve, when implanted, permits blood flow towards the atrium fromthe second vein and the fourth vein, and prevents blood flow from theatrium to the second vein and the fourth vein.
 58. The apparatus ofclaim 46, wherein the first stent is configured to provide a largerradial force at the distal end of the first stent than at the proximalend of the first stent when expanded, and wherein the second stent isconfigured to provide a larger radial force at the distal end of thesecond stent than at the proximal end of the second stent when expanded.59. The apparatus of claim 46, further including: a third stent having athird valve coupled thereto, the third stent configured for implantationin a third vein leading to the atrium such that, when implanted, aproximal end of the third stent extends into a portion of the atrium,and a distal end of the third stent extends into a portion of the thirdvein; and a fourth stent, having a fourth valve coupled thereto, thefourth stent configured for implantation in a fourth vein leading to theatrium such that, when implanted, a proximal end of the fourth stentextends into a portion of the atrium and a distal end of the fourthstent extends into a portion of the fourth vein.
 60. The apparatus ofclaim 59, wherein: the first, second, third, and fourth valves permitblood flow toward the atrium from a respective one of the first, second,third, and fourth veins; and the first, second, third, and fourth valvesprevent blood flow from the atrium to a respective one of the first,second, third, and fourth veins.
 61. The apparatus of claim 60, whereinthe distal end of the first stent extends into a portion of a third veinwhen implanted, and wherein the distal end of the second stent extendsinto a portion of a fourth vein when implanted.
 62. The apparatus ofclaim 59, further including: a first bracing element coupled to thefirst and second stents; a second bracing element coupled to the thirdand fourth stents; a third bracing element coupled to the first andthird stents; and a fourth bracing element coupled to the second andfourth stents.
 63. An apparatus comprising: a first stent configured forimplantation relative to a first pulmonary vein and a third pulmonaryvein, each of the first and third pulmonary veins leading into theatrium, the first stent including a first valve; and a second stentconfigured for implantation relative to a second pulmonary vein and afourth pulmonary vein, each of the second and fourth pulmonary veinsleading into the atrium, the second stent including a second valve;wherein the first valve, when implanted, permits blood flow towards theatrium from each of the first and third pulmonary veins, and preventsblood flow from the atrium to each of the first and third pulmonaryveins; and wherein the second valve, when implanted, permits blood flowtowards the atrium from each of the second and fourth pulmonary veins,and prevents blood flow from the atrium to each of the second and fourthpulmonary veins.
 64. An apparatus comprising: an expandable first stentincluding a first valve, the first stent configured for implantation ina first vein leading to an atrium of a heart such that, when implanted,a proximal end of the first stent protrudes into a portion of theatrium, and a distal end of the first stent extends into a portion ofthe first vein, wherein a fully-expanded diameter of the proximal end ofthe first stent is smaller than a fully-expanded diameter of the distalend of the first stent; and an expandable second stent directionallyopposed to the first stent, the second stent including a second valveand being configured for implantation in a second vein leading to theatrium such that, when implanted, a proximal end of the second stentprotrudes into a portion of the atrium, and a distal end of the secondstent extends into a portion of the second vein, wherein afully-expanded diameter of the proximal end of the second stent issmaller than a fully-expanded diameter of the distal end of the secondstent.
 65. The apparatus of claim 64, wherein the first valve isattached to the proximal end of the first stent such that, whenimplanted, at least a portion of the first valve extends into theatrium, and wherein the second valve is attached to the proximal end ofthe second stent such that, when implanted, at least a portion of thesecond valve extends into the atrium.